Optical fibers are used in an ever-increasing number of applications for transmitting data signals. An optical fiber is a thin transparent strand of material that acts as a waveguide for light. Optical fibers have several advantages over traditional copper conductors, including their light weight, high bandwidth, smaller size, immunity from electromagnetic interference, and low signal attenuation over long distances. Owing to these characteristics, optical fibers are particularly useful for providing a physical transmission medium for communications links and have replaced copper conductors in many communications applications. The small size, light weight and superior performance characteristics of optical fiber or “fiber-optic” cables also makes them attractive to the aerospace industry for both commercial and military applications.
Because the individual strands of optical fibers are fragile, they are usually configured into an overall larger optical cable for practical applications. An optical cable may contain one or more optical fibers, and has a construction that provides mechanical strength and protection from environmental stresses so that the optical fiber may be used reliably in harsh environments. Generally, a fiber optic cable includes a core made of a glass strand, or fiber, that is surrounded by a cladding layer and one or more additional layers. The cladding layer contains optical signals in the glass core. The cladding may also provide color coding so that individual fibers can be identified when making connections in a fiber-optic cable containing more than one optical fiber. One or more additional coatings or buffer layers may then be provided to buffer and support the cladded fiber core. Additional strength member layers may be utilized outside the buffer layers to provide resistance to pulling and other mechanical forces. Finally, an insulated jacket layer may be added to provide a protective outer surface to resist abrasion and other environmental conditions.
Aerospace applications in particular present demanding requirements for fiber-optic cables in both size and weight considerations. Typically, the space within an aircraft is limited and thus the weight and size of cables running throughout an aircraft is always of utmost concern. Furthermore, there are harsh conditions inherent in such operational and installation environments. Still further, even minor failures in the fiber-optic cable can result in significant, undesirable consequences. Operational conditions typical of an aerospace environment typically include high levels of vibration, mechanical stresses, temperature extremes, g-loading, and submersion in caustic fluids. In particular, with regard to the installation environment, it is desirable for a fiber-optic cable used in an aerospace application to tolerate tight bend radiuses, crushing forces, caustic fluids and temperature extremes. Installation within the confined spaces presented by an airframe can subject a fiber optic cable to tight bends, high pinching and crushing forces, as well as high pulling stresses as installers manipulate the cable. Severe bending or forcing the cable around a small radius may result in a kink in the cable, which may result in reduced light transmission sufficient to render the cable inoperative. These performance requirements may present conflicting design choices in providing suitable fiber-optic cables. For example, a fiber-optic cable that is designed to withstand high crushing and pulling forces may be too thick to meet bend radius requirements or too difficult to install. Designing fiber-optic cables for aerospace applications is further complicated by constraints on the choice of materials available that satisfy safety requirements, such as low production of smoke and toxic chemicals when subjected to fire. Aerospace applications, as noted, are also particularly sensitive to size and weight concerns.
It is therefore desirable to improve generally upon fiber-optic cable technology to address the issues noted above and to provide greater resistance to damage from environmental and installation stresses. It is also desirable to reduce the impact of crushing, pinching, kinking or otherwise compromising the mechanical structure of a fiber-optic cable on the ability of the optical fibers to transmit light. It is further desirable to provide a fiber-optic cable in a form factor that facilitates installation while remaining compatible with standard multi-strand fiber-optic ribbon cable connectors.